Air expansion power system



Feb 5, 1946- F. NETTEL Erm.

AIR EXPANSION POWER SYSTEM Filed. July 10, .941 3 Sheets-Sheet 1INVENFORS Peb 5, 1945- F. NETTELl-:rAL 2,394,253

AIR EXPANSION POWER SYSTEM Filed July 10, 1941/' 3 Sheets-Sheet 2 Feb.5, 194s. F, NETTL mL 2,394,253

vAIR ExANsIo-N POWER SYSTEM Filed July 10, 194i '-3 sheets-sheet 3fPatented Feb. 5, 1946 AIR MANSION lfwER SYSTEM Frederick Nettel,Manhasset, and Johann Breitner, New York, N. Y.

Application July 10, 1941, Serial N0. 401,703

,9Claims.

The present art of expansion power systems uses open cycles with heatingof the working medium by internal combustion of fuel in it, or closedcycles with heating through heating surfaces.

Closed cycles can utilize any type of fuel, but they are suering frommany defects which impeded their practical use.

The broad object of this invention is to avoid these defects, simplifythe arrangement and to improve the emciency.

It is a further specific object of this invention to provide a powersystem for double fuel operation.

The broad object is achieved by burning the fuel in a portion oi' theexpanded air branched oil? after passing through part or the whole ofthe heat exchanger and by leading the gases and the exhaust air inseparate streams through said heat exchanger and thence to theatmosphere.

Pure air only is working in the expansion machine. The temperature limitfor the heated air is mostly dictated by the blading material of theturbine, and the surface heaters are designed for said limitingtemperature. There are, however, other cases, where the metallurgicalproperties of the tube material of said heaters restrict the airtemperature at the heater outlet to lower values than the turbineblading can stand. Since the overall thermal emciency of'air expansionpower plants rises sharply with increasing turbine inlet temperature,this invention includes a combination of indirect heating as describedhereinbefore, with additional direct heating by internal combustion.According to this invention, the bulk of the heat input is supplied byburning cheap fuel, for example coal, in air discharged from theturbine, and the combustion heat transferred through heating surfaces tothe compressed air, which is thus heated 11p to the metallurgical limitfor the heater tubes. Thereafter a comparatively small quantity of fuelsuitable for internal combustion, namely one whichburns practically freefrom ash, residue or other deleterious concomitants, is injected intothe hot compressed air and burned therein, whereby the air is heatedfurther, up to the temperature permissible for the turbine blading. Suchdouble fuel ,operation may be continuous or only temporary, such as forinstance in power plants where base load is' produced by burning cheapfuel, and peak `load by additional internal combustion of gaseous orliquid fuel in an internal combustion chamber disposed in iront of theturbine inlet.

In the drawings amxed to this specication and forming part thereof,several embodiments oi this Fig. 3 represents an alternative embodimentof the regenerative heat exchanger.-

Fig. i shows a modification of Fig. 2 with subdivided combustion chamberserved by two travelling gratos and an induceddraft fan for the easesdischarged from the heat exchanger.

Fig. 5 represents a modication of Fig. 1 with the furnace air branchedofi behind the regenerative heat exchanger and fed back into the airpipe from the turbine before said heat exchanger, and an additionalinternal 'combustion chamber ior burning liquid fuel during double fueloperation. i

The plant according to Fig. 1 operates as follows: Airis taken in at iinto the first stage compressor 2, cooled in the interccoler 3,compressed further in the second stage compressor t, from which it Howsinto the tube system of the regenerative heat exchanger 5, in which itis preheated as will be explained hereafter. From E it ilows throughpipe t and through the heating coil l, which latteris arranged withinthe combustion chamber t, and through pipe ii to the air turbine it,where it expands to a pressure near the atmospheric pressure whiledeveloping mechanical power to drive the compressors 2 and t and theelectric generator il, which latter supplies useful power. The expanded,but still very hot air leaves turbine lil at i2 vand flows partlythrough the heat exchanger 5 where it is used to preheat the compressedair before being discharged to the atmosphere at i3. `another part ofthe hot air discharged from the turbine flows via a regulating ilap itand duct le to the combustion chamber t where it is used in the burnerit, supplied with pulverized coal from source il, to heat the compressedair owing through the heating coil i disposed within said combustionchamber. The combustion gases formed in chamber ii leave the latter atI8 to flow through the regenerative heat exchanger 5, where they alsoheat the compressed air within the tube system before being expelled tothe atmosphere at it. Cooling water for'the intercooler enters at it andis discharged at 2i. From air duct i5 a branch duct 22 leads directlyinto d with flap valve it arranged at the branching point. Fuel valve2t, which opens when turned anti-clockwise, is coupled by linkage asshown to thermostat 25 with elastic bellows 26 and to yball governor 21.The latter is driven from turbine shaft.

Load and temperature regulation is effected as I follows: Withincreasing load the governor sleeve 29 moves downwards while point 30,which is connected to the thermostat bellows, remains stationary duringthe first moments. Thus point 28 also moves downwards with the resultthat fuel valve 24 opens and flap 23 admits more air to the burner. Theincreased heating causes the temperature at 25 to rise and the bellowsto.

-time acts as safety device against excess speed and excess airtemperature in coil 1.

While for pulverized coal ring highly preheated combustion air is veryadvantageous, the temperature of such air for grates is limited bydesign reasons to about 200 deg. C. For such plants the method of airsupply is modified as will be shown in Fig. 2.

The power plant as per Figure 2 operates as follows: Air is taken infrom the atmosphere at 3 I, compressed' in first stage compressor 32,intercooled in cooler 33, which` is shown in the example as of the waterspray type in which cold water is sprayed in counterilow to thecompressed air as indicated in Fig. 1 in more detail. The air is furthercompressed in second stage compressor 34, flowing hereafter through thetube system of the regenerative heat exchanger 35, thence through pipe36 into the heating coil 31, arranged within the combustion chamber 38,and through pipe 39 into the first stage air turbine 40 which drives theelectric generator 4|. From turbine 40 the air ows in a partly expandedcondition through a second heating coil 31', also disposed within saidcombustion chamber 38, in which the air, is reheated, flowing hereafterthrough the second stage turbine 4U' in which it expands to a pressurenear the atmospheric pressure while delivering mechanical power todrive'part compressors 32 and k34, and is finally expelled in part at 43into the ambient atmosphere. The remainder of-that air is, however.branched oil behind the heat exchanger via nap valve 44 into duct 45,which leads it under the travelling grate 46 disposed in combustionchamber 38, thus supplying warm air for the combustion of the coalwhich' is fed to said travelling grate from coal chute 41. Thecombustion gases formed in 38 leave it at 48 to ow also through theregenerative heat exchanger 35, in which they also preheat thecompressed air coming from compressor 34, to be hereafter expelled tothe atmosphere at 49. For load regulation it may be desirable toregulate the heating of the air in coils 31 and` 31 independently. Insuch cases it is advantageous to provide separate grate, stokers or forpulverized coal firing separate burners, for each of the heating coils.

The principal difference between the arrangements shown in Fig. 1 andFig. 2, as regards. the surface heaters, consists in the combustion airbeing branched off before the regenerative heat exchanger in Fig. 1 andafter the heat exchanger 35 in Fig. 2.

In some cases it is desired to supply the air for the combustion chamberat a temperature below that at which it is discharged from the turbinebut higher than that at which it leaves the heat exchanger. For thispurpose the regenerative heat exchanger is modified as shown in Fig.l 3.'I'he air discharged from the air turbine enters at 60, ows as indicatedby dotted line up to the outlet branch 6i provided with a ap valve 62.At this point part of the air is branched oi to the combustion chamber(not shown) while the remaining portion ows on through the whole lengthof the heat exchanger, leaving it at 63. The combustion gases from thecombustion chamber enter at 64 and ow as also indicated by dotted line,through the whole length of the heat exchanger, leaving it at 65.

The plant as per Fig. 4 operates generally in the samermanner as that ofFig. 2. -The combustion chamber, however, is sub-divided by a wall 38'into two part-chambers in communicating connection at the top. Eachpart-chamber is served by its own travelling grate, 46' and 46" to whichair is fed through pipes 45' and 45" respectively. The two grates permitto control vthe heating in the coils 31 and 31 indithe heat exchanger35, an induced draft fan 49' is disposed in the outlet pipe 49 from saidheat exchanger.

The plant as per Fig. 5 operates in principle in the same manner as thatshown in Fig. l. However, the air for the combustion chamber 8 isbranched oil' behind the heat exchanger 5E, through pipe l5', fan I5",pipes 22 and the coal burner I6 into the combustion chamber 8. The gasesleave lthis chamber by pipe I8' and are led into the pipe coming fromthe air turbine I0, where they mix with the air discharged from saidturbine. 'I'he branched-olf air is not quite pure, containing a verysmall quantity of combustion products, which, however, have no effectson the combustion in chamber 8. Another special feature of this exampleof the invention consists in the provision of the internal combustionchamber 52, disposed' in pipe 9, in which additional liquid fuel isburned to heat the Working air to a higher temperature than is done inheater coil 1. This liquid fuel is fed to chamber 52 from fuel tank 56via fuel pump 55, pipe 54 with regulating valve 53. Thus part of theheat required in the system is produced by pulverized coal in anexternal furnace, and another part by liquid fuel in an internalcombustion chamber.

It is immaterialto this invention what types of turbines, expansionengines, compressors, coolers, regenerative heat exchangers andcombustion devices are used and what kind of fuel is burned in thelatter. y

Manifestly, variations may be resorted to, equivalents of partsintroduced, and parts may be used without others within the broad scopeof the invention and its features.

Having now described our invention, we claim:

1. In the method of producing power by successively compressing, heatingand expanding a gaseous working uid, the combination of com- A pressingan air stream, preheating it by surface heat transfer from said samestream after its expansion, heating it further by surface heat transferfrom the gaseous products of an external fuel combustion eiected atsubstantially atmospheric pressure, heating it still further by internalcombustion of fuel in said compressed air, expanding the resultingcompressed and heated air-gas mixture to substantially atmosphericpressure, thereby developing power, cooling said air-gas mixture by saidsurface heat transgases by said surface heat transfer to said compressed air, and ejecting said cooled combustion gases to theatmosphere.

2. In a powersystem including means to take in a continuous stream ofair from the ambient atmosphere, means to compress it, regenerativeheatI exchange means to preheat it after compression, surface type fuelburning means to heat it further, an expansion machine disposed todevelop power by expansion of said compressed and heated air, conduitmeans connecting in succession, the outlet of said compressing means tothe inlet of the heated side of said heat exchange means, the outlet ofthe latter to the inlet of said fuel burning heating means, the outletof the latter to the inlet of said expansion machine, the outlet of thelatter to the inlet of the heating side of said heat exchange means, theoutlet of the latter to the atmosphere, conduit means for branching offa portion of th expanded air after it has passed through saidregenerative heat exchange means, and for leading it to said fuelburning heating means so as to use said branched oi air as combustionair, said heating means being designed for air inlet temperatures under200 deg. C.

3. In a power system including means to take in a continuous stream ofair from the ambient atmosphere, means to compress it in stagecompressors with interposed cooling means, regenerative heat exchangemeans to preheat said air after compression, surface type fuel burningmeans to heat it further, an expansion machine disposed to developuseful power by partial expansion of said compressed and heated air,second surface type fuel burning means to reheat the air issuing fromsaid expansion machine, a second expansion machine disposed to developpower for driving said compressors by expansion of the partiallyexpanded reheated air to nearatmospheric pressure, conduit means forconnecting in succession, the outlet of the highest pressure stagecompressor to the inlet of the heated side of said heat exchange means,the outlet of the latter to the inlet of said first surface type fuelburning heating means, the outlet of the latter to the inlet of said rstexpansion machine, the outlet of the latter to the inlet of Iii) saidsecond surface typefuel burning reheating being designed for air inlettemperatures under' 290 deg. C.

e. In a power system according to claim 3, hrst and second surface typefuel burning heating and reheating means for the air being independentof each other as regards adjustment of iiuel feed.

5. In a power system including means to take in a continuous stream ofair from the ambient atmosphere, means to compress it, regenerative heatexchange means to preheat it aftercompression, surface type fuel burningheating means to heat it further, an expansion machine disposed todevelop powerv by expansion of said compressed and heated air, conduitmeans for connecting in succession, the outlet of said compressing meansto the inlet to the heated side of said heat exchange means, the outletof the latter to the inlet of said fuel burning heating means, theoutlet of the latter to theinlet of said expansion machine, the outletof the latter to the inlet of the heating side of said heat exchangemeans, the outlet of the latter to the atmosphere, conduit means -forbranching/off a portion of the expanded air Aafter it has passed throughsaid regenerative heat exchange means, and for leading it to said fuelburning means so as to use said branched oif air as combustion air,conduitv means for leading the products of combustion from said fuelburning heater to the heating side of said regenerative heat exchangemeans, and flow dividing means in said regenerative heat exchange meansto allow the air issuing from said expansion machine and the products ofcombustion from the fuel burning heater to ilow in separatesubstantially parallel streams through the heating side of saidregenerative heat exchange means.

6. In a power system including means to take in a continuousstream ofair from the ambient atmosphere, means comprising stage compressors y tonear-atmospheric pressure, conduit means for z connecting in succession,the outlet of the highest pressure stage compressor to the inlet of theheated side of said heatexchange means, `they outlet of the latter-tothe inlet of said rst fuel burning heating means, the outlet of thelatter to the inlet of said rst expansion machine, the outlet of thelatter to the inlet of said second fuel burning reheating means, theautistof the latter to the inlet of said se i wpai/:reilen machine, theoutlet of the latter to the inlet of the heating side of said heatexchange means, the outlet of the latter to the atzc'icsphere, conduitmeans for branching o@ a portion of the expanded air after it `haspassed through said regenerative heat exchange means, and for leading it.v to both said fuel burning heating and reheating means so as to usesaid branched on@ air as combustion air, conduit means for leading theproducts of combustion in said fuel burning heaters to the heating sideof' said regenerative heat exchange means, and flow dividing 'means insaid regenerative heat exchange means te allow the air issuing from saidsecond expansion machine and the products of combustion from the fuelburning heaters to flow in' separate substantially parallel streamsthrough the heating side of said regenerative heat exchange means.

7. In a power system according tc claim 6, rst and second surface typefuel b heatv it further, an expansion machine disposed to develop powerby expansion of said compressed and heated air, conduit means forconnecting in succession, the outlet of said compressing means to theheated side of said heat exchange means,

' the outlet of the latter to the inlet of said fuel burning heatingmeans, the outlet of the latter to the inlet of said expansion machine,the outlet of the latter to the inlet of the heating side of said heatexchange means, the outlet of the latter to the atmosphere, conduitrmeans for branching oil' portion of the expanded air after it has passedthrough said regenerative heat exchange means, and for leading it tosaid fuel burning heating means so as to use said branched oir air ascombustion air, and conduit means for leading the products of combustionfrom said fuel burning heater into the heating side of said regenerativeheat exchange means, so as to admix them to the air issuing from saidexpansion machine.

` 9. In the method of producing power by successively compressing,heating and expanding a gaseous working fluid, the combination ofcompressing an air stream, preheating it by surface heat transfer fromsaid same stream after its expansion, heating it further by surface heattransfer from the gaseous products of an external fuel combustioneffected at substantially atmospheric pressure, expanding the compressedand heated air to substantially atmospheric pressure thereby developingpower, cooling said expanded air by said surface heat transfer to saidlcompressed air stream, ejecting a portion of said expanded and cooledair to the atmosphere, utilizing the remaining portion of said expandedand cooled air as combustion air for said external combustion, coolingthe resultant combustion` gases by said surface heat transfer to saidcompressed air stream, and ejecting said cooled combustion gases to theatmosphere.

FREDERICK NE'I'IEL. JOHANN KREITNER.

